1. Field of the Invention
The invention relates to wireless communication systems, and in particular to a device and method of calculating output power in a wireless communication system.
2. Description of the Related Art
When a mobile station (MS) transmits data, it is required to control the power of transmitting data to reduce the transmission power, as well as to maintain a satisfactory level of data transmission quality.
FIG. 1 shows output power of a transmitter compliant to 3GPP Standard, where the horizontal axis represents time and the vertical axis represents output power. For each power control level (PCL), 3GPP Standard specifies a corresponding output power limit. For each data burst, the output power increases in Stage 10, remains substantially constant in Stage 12, and decreases in Stage 14. The power ramp-up and ramp-down corresponding to Stages 1 0 and 14 can reduce signal interferences and noises, thereby increasing the data transmission quality. A transmitter transmits data with an output power selected by a power control level during Stage 12. The duration of Stages 10, 12, and 14, and the ramp-up and ramp-down power are clearly specified in the associated telecommunication specification.
The prior art utilizes a lookup table that establishes a number of estimates approximating ramp output power for each selected power control level. A mobile station reads a corresponding ramp output power estimate upon receiving a power control level to generate the ramp in Stages 10 and 14. Unfortunately, the prior art requires large memory resource for storing the estimates of ramp output power, and processing power for accessing the estimates to generate the ramp output in Stages 10 and 14.
Thus a need exists for a device and method of calculating output power to utilize system resources efficiently.